Significance: Glucocorticoid (GC) treatment, a common anti-inflammatory prescription for rheumatoid arthritis, has a dangerous side effect: it elevates risk for osteoporosis and bone fracture. To reduce this effect, other drugs are being tested in combination with GC. The efficacy of these cocktails is often studied in a transgenic mouse model of rheumatoid arthritis, using X-ray imaging and mechanical tests to assess bone quality. Unfortunately, radiographic density correlates only weakly with early stages of bone fragility, and mechanical tests require sacrifice of the animal and cannot be translated to human patients. New methods are needed to study the progression of bone deterioration in animals (and humans) over time, particularly to detect alterations in the early stages where intervention is most valuable. Innovation: We propose the use of Raman spectroscopy (RS), a chemically-sensitive optical scattering technique, to monitor bone quality through the intact limbs of living, GC-treated mice. In preliminary tests, Raman spectra of excised bones from such mice exhibit lower mineral-to-matrix ratios than from control animals, and the ratio correlates strongly with mechanical tests of bone strength. Separate tests have verified that Raman signatures from mouse bones can be gathered through the soft tissue of intact limbs. These results motivate the hypothesis that RS can monitor individual mice noninvasively at multiple time points and detect early signs of bone alteration under various GC treatment regimens. As an added benefit, no ionization radiation is used, unlike the common microCT and DXA (dual X-ray absorptiometry) modalities. Specific aims: The project's first specific aim is to identify the Raman spectral features from ex vivo cortical bone that correlate most strongly with gold-standard assays of bone quality. Groups of mice will be paired to study three variables: wild-type vs. transgenic, GC-treated vs. placebo, and GC-alone vs. GC-plus- drug. The second specific aim is to obtain this same Raman information transcutaneously in living animals, using optimized probe geometry and data analysis to reduce interference from overlying soft tissue. Achieving this aim will enable robust monitoring of bone quality in individual animals over several weeks, producing histories of bone fragility onset in individual mice with unprecedented detail. Such histories should be rich sources of information about how GC treatment compromises bone quality and about the preventive capabilities of complementary drugs, providing feedback for disease management and treatment. Relevance: The proposed work directly addresses NIBIB's mission of developing technologies for early disease detection and assessment of health status, as well as NIAMS's mission to support research into the causes, treatment, and prevention of arthritis and musculoskeletal and skin diseases. PUBLIC HEALTH RELEVANCE: People with rheumatoid arthritis are often given medications to reduce the inflammation. Unfortunately, these medications themselves have side effects that elevate risk for bone fracture. This study will develop a noninvasive optical method of measuring bone fragility in arthritic mice as they receive both anti-inflammatory medication and complementary drugs that try to preserve bone health. By providing a better way of tracking bone fragility in living animal models, this work will generate new understanding of how bone disorders develop and how medicines can treat them more effectively in both animals and humans.